Raised pavement markers offer a greater degree of night delineation, wet or dry, than is offered by painted lines and tapes. They are raised up out of the rain on the street, and they are able to present reflective materials at a more advantageous angle to drivers than flat tapes. However, in areas where snow plows are used, they have not found wide acceptance because they either are removed or damaged by the plows or can damage plow blades.
One solution to the problem of designing a durable pavement marker for snow plow areas is presented in U.S. Pat. No. 4,297,051. That patent shows a deformable highway marker comprising a flexible, cylindrical skirt portion for implanting in a road; a dome-shaped top portion integrally molded with the skirt, for extending above the roadway surface; and a reflecting means associated with the top portion. The dome-shaped top is shown to elastically deform downward when traversed by a snow plow blade, recovering its original shape after the blade has passed.
Although the '051 marker represented an advance in the art, there remained difficulties with its design. It lacked desired durability, and it was difficult to reflectorize.